Delay compositions and detonation delay devices utilizing same

ABSTRACT

A delay composition for a detonator or delay device. The composition comprising a mixture of silicon and barium sulfate, and an amount of red lead in the range of about 3 to 15%, and preferably 6 to 12%, by weight of the mixture. The invention also relates to a delay element comprising a rigid metal tube containing the delay composition, and a delay device incorporating the delay element.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of applicant's copending U.S. patentapplication Ser. No. 09/895,334, filed Jul. 2, 2001.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates to delay compositions used in detonators forexplosives (sometimes referred to as blasting caps) and other devices(e.g. inline detonation delay devices), and to detonation delay elementsand devices containing such compositions. More particularly, theinvention relates to delay compositions having slow-burning (long delay)times for use with both non-electric and electric detonators, inlinedelay devices, and the like.

II. Background Art

Delay compositions are materials that burn away rapidly, but notinstantly, when ignited, thus create a timing delay, in the nature of afuse, when shaped and compacted in the form of an elongated body orcolumn and ignited at one end. Such compositions may therefore be usedto create a delay between the instant at which a detonator or similardevice receives a firing signal (which commences ignition of the columnof delay composition), and the instant at which an associated explosivecharge is set off (by heat when the combustion reaches the remote end ofthe burning column), or a further firing signal is generated.

Delay detonators and similar delay devices, both non-electric andelectric, are widely employed in mining, quarrying and other blastingoperations in order to permit sequential initiation of explosive chargesdistributed in a predetermined pattern of bore holes or shot holes. Theprovision of a delay between sequential initiation of adjacent bore orshot holes is effective in controlling the fragmentation and throw ofthe rock being blasted and, in addition, provides a reduction in groundvibration and in air blast noise.

Modern commercial delay detonators, whether non-electric or electric,normally comprise a metallic shell, closed at one end, which contains insequence from the closed end: a base charge of a detonating highexplosive, such as for example pentaerythritoltetranitrate (PETN), andan adjacent primer charge of a heat-sensitive detonable material, suchas for example lead azide. Adjacent to the heat-sensitive material is aconsolidated, e.g. compressed, column of delay composition of sufficientlength and quantity to provide a desired delay time as described above.The column of the delay composition is normally confined within a hollowtubular confinement element made of metal. The confinement element anddelay composition contained therein, together with sealers and primercharges, if any, form a delay element that is normally fabricatedseparately and assembled into a detonator or the like as a single item.Next to the delay element is an ignition (starter) charge adapted to beignited by an electrically heated bridge wire or, alternatively, by theheat and flame of a low energy detonating cord or shock wave conductorretained in the open end of the metallic shell. Such a delay detonatormay serve as an in-line delay as when coupled at both ends to adetonating cord or shock wave conductor. However, a delay device neednot also be capable of serving as a detonator in order, for example, toinitiate a shock wave conductor. An ignition charge in close proximityto the end of the shock wave conductor, instead of a base charge ofdetonating high explosive, will suffice.

The containment of the delay composition within a confinement elementfacilitates the handling of the composition and its introduction into adetonator or the like. The metal also protects other components (e.g.the outer shell of a detonator) from the heat and by-products ofcombustion as the delay composition is consumed and, for reasons ofeconomy, minimizes the amount of the delay composition that is required.In the past, lead has often been used as the metal for the confinementelements. Lead is soft and malleable and can be loaded with a burningcore, drawn to a desired diameter and cut to required lengths (differentlengths produce different delay times). Lead also has a low thermalconductivity and heat capacity, and therefore diverts only a minimumamount of heat from the composition as it burns, thus reducing the riskthat the combustion may be quenched or extinguished prior to completeconsumption of the delay composition.

A trend has recently developed of replacing confinement elements made oflead with elements made of rigid metals, such as zinc, aluminum, steelor brass. Zinc is currently the preferred metal of choice for thispurpose. The term “rigid metal” refers to those metals that, when usedto form confinement elements, are not easily drawn to a desired diameteror shaped using the equipment currently available for lead. With suchmetals, the confinement elements are first cast to the desired diameterand length, and then the delay composition is loaded into the interiorof the element and compressed. This change to rigid metal confinementelements has come about in part because the use of lead is receivingcriticism from some quarters for being environmentally hazardous, eventhough the quantity of lead is small. Moreover, the use of rigid metalconfinement elements can facilitate fabrication of delay units and theirintegration into detonators and delay devices, etc. However, zinc andother suitable rigid metals have higher thermal conductivities and heatcapacities than lead, and thus extract more heat from the delaycomposition as it burns. This can increase the failure rate ofdetonators and delay devices because there may be insufficient heatremaining in the delay composition to maintain the combustiontemperature until complete consumption of the composition has takenplace, especially when such devices are used in low temperatureenvironments. Particularly at risk of failure are delay units intendedto provide long delays, e.g. more than one second, often used inunderground applications.

A large number of delay compositions are known in the art. Thesegenerally comprise mixtures of fuels and oxidizers of various kinds.Many are substantially gasless compositions, which are generallypreferred; that is, they burn without evolving large amounts of gaseousby-products which could interfere with the functioning of a delaydetonator or other device. In addition to an essential gaslessrequirement, delay compositions are also required to be safe to handle,from both an explosive and health viewpoint, they must be resistant tomoisture and not deteriorate over long periods of storage and hencechange in burning characteristics, they must operate reliably over awide range of temperatures, and they must be adaptable of use in a widerange of delay units within the limitations of space available inside astandard detonator shell or similar device. The numerous delaycomposition of the prior art have met with varying degrees of success inuse and application.

One such prior class of delay compositions intended for use inconfinement elements made of lead is that described in U.S. Pat. No.4,419,154 to Davitt et al. (assigned to CXA Ltd/CXA LTEE) which issuedon Dec. 6, 1983. This patent discloses a composition comprising siliconand barium sulfate and optionally including a proportion of particulatered lead (lead tetroxide, Pb₃O₄) in the amount of 25 to 75% by weight ofthe composition. The compositions of Davitt which include red lead canbe used in confinement elements made of lead to produce intermediate tolong timing delays. However, in order to achieve the long timing delayswith red read, which is recognized as a strong oxidant, the Davittcompositions have to be prepared with coarse silicon. Such slow burningcompositions are difficult to ignite due to the use of such coarsesilicon that goes against traditional pyrotechnic principles as taughtby Professor Conkling, who stated, in Chemistry of Pyrotechnics, John A.Conkling, Marcel Dekker Inc., 1985, pp 88-89:

-   -   “Homogeneity, and pyrotechnic performance, will increase as the        particle size of the various components is decreased. The finer        the particle size, the more reactive a particular composition        should be, with all other factors held constant.”

Furthermore the slow burning compositions of Davitt et al. with red leadwere prepared with a very small ratio of the fuel component (i.e.silicon) which was significantly below the stoichiometric ratio, withthe consequence of reducing the energy output of the combustion process.Such formulations would not be robust in various conditions, such aswhen used in rigid elements as herein described where the thermalconductivity of such confinement materials is significantly higher thanlead. Furthermore, when Davitt et al. attempted to use finer siliconwith red lead, which would have had the consequence of improving thepyrotechnic performance, significantly faster timing results wereobtained (Column 8 of the patent). The only slow burning compositions ofDavitt et al. that can be prepared with fine silicon are those withoutred lead. Thus, according to Davitt et al., compositions with red leadare not ideal for producing long timing delays. For long delay periods,there is therefore a need to find alternative delay compositions.

U.S. Pat. No. 5,147,476 to Beck et al. (assigned to Imperial ChemicalIndustries PLC), which issued on Sep. 15, 1992, addresses the problem ofincreasing the robustness of combustion of delay compositions intendedfor use in rigid metal confining elements to reduce the likelihood ofquenching of the combustion. The concept of Beck et al. was tofacilitate the combustion of a mixture of silicon and barium sulfate (orother oxidant) by adding small amounts of dispersed metal compounds toserve as reaction-facilitating fluxes (i.e. materials that lower thefusion temperature of the composition, but are otherwise inert). Theillustrated metal compounds are salts of alkali metals, oxides ofantimony and oxides of vanadium. Beck et al. found that for reliableburning of such a composition, the heat sink effect of the confinementmetal element should not be such as to risk quenching of the exothermicreaction (i.e. burning) of the delay composition. However, the delaycompositions of the kind disclosed by Beck et al. do not work as well asmight be desired, particularly when used for producing long delays.Moreover, the oxides used in these compositions as fluxes are expensive.Beck et al. suggested that additions of red lead oxide or other reactiveingredients that cause a faster rate of burning may be incorporated intothe composition, but noted that large loadings of such reactiveingredients may obviate the facilitating role of the flux. Beck et al.therefore recommended that the compositions omit such additionalreactive ingredients.

There is therefore a continuing need for a delay composition that can beused reliably when confined in rigid metal confinement elements and yetmay be used to produce long delays without unacceptably increasing thelengths of delay units.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a delay compositionthat may be confined within a rigid delay element and yet still undergoreliable ignition and burning capable of producing long timing delays.

Another object of the invention is to provide a delay composition of thestated kind that can be produced easily and inexpensively.

Yet another object of the invention is to provide delay devices that arereliable in that they ignite and burn continuously with a high degree ofreliability, even at low temperatures, and provide a reliable long delayperiod.

Another object of the invention is to provide delay elements anddetonators or similar devices capable of providing long delay timeswhile making use of rigid confinement elements for delay compositions.

According to one aspect of the present invention, there is provided adelay composition comprising mixed particles of silicon, barium sulfateand red lead, the red lead being present in an amount of about 3 to 15%by weight, preferably 6 to 12%, and more preferably 9 to 12% by weight,of the composition.

The barium sulfate and silicon components are preferably present inamounts of 40 to 65% by weight and 50 to 25% by weight, respectively, ofthe total weight of the composition.

The composition preferably also contains a binder causing collections ofthe particles to bind together in the form of free-flowing granules. Thebinder is preferably present in amounts of 0.2 to 0.6% by weight of thecomposition. Suitable binders include solvent-soluble polymers, silicaand swelling clays, preferably water-soluble derivatives of cellulose,e.g. carboxymethyl cellulose.

According to another aspect of the invention, there is provided a delayelement for a detonator or delay device, comprising an elongated hollowmetal tube containing a delay composition comprising mixed particles ofsilicon, barium sulfate and red lead, the red lead being present in anamount of about 3 to 15% by weight of the composition. The tube ispreferably open at both ends, and is preferably made of a rigid metal,most preferably zinc. The delay composition is preferably compressed toa density in the range of 1.8 to 2.2 g/cc, more preferably 1.95 to 2.15g/cc.

The delay element preferably includes a sealer at one end thereof (theend subject to combustion first). This is may be a type of pyrotechniccomposition that forms a slag of material which seals the open end ofthe delay element. This is desirable as the burn rate of the delaycomposition may be pressure-dependent and uniform delay times can beachieved when the sealer regulates the pressure within the delayelement.

The delay element may also have a starter composition at the same end.The purpose of the starter composition is to generate enough heat toreliably initiate the slow burning delay composition having a highignition temperature. A single composition may server both the functionof a starter composition and of a sealer composition.

According to yet another aspect of the invention, there is provided adelay device, such as a detonator or inline delay device, comprising adetonation signal input, a charge to be detonated by the detonationsignal input, and delay element separating said detonation signal inputand said charge, the delay element being an element of the typedescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-section of an example of a non-electricdetonator incorporating a delay element containing a delay compositionof the present invention;

FIG. 2 is a vertical cross-section of an example of an electricdetonator incorporating a delay element containing a delay compositionof the present invention; and

FIGS. 3 to 20 are graphs showing results obtained in the ways describedin the following Examples.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 of the accompanying drawings shows an example of a non-electricdelay detonator 10 of a kind with a delay element and delay compositionaccording to the present invention may be employed. As such, thedetonator itself forms an example of one aspect of the presentinvention.

The detonator 10 has a metallic tubular detonator shell 11 closed at itsbottom end and containing a base charge 12 of explosive (e.g. PETN)pressed or cast therein. Immediately above the base charge 12 is aconfinement element 14 made of a rigid metal such as zinc, aluminum,steel or brass (preferably zinc). The confinement element 14 contains aninitiating charge 15 (e.g. of lead azide) at the lower end of theelement, and a delay composition 16 within the delay element above theinitiating charge 15. The confinement element and its contents,particularly the delay composition, together form a delay element 14 athat is fabricated prior to the assembly of the detonator. A starterelement 17, which preferably also acts as a sealer, is located above thedelay element. A lower end of a bore in the starter element contains astarter charge 18. An anti-static cup 19 is positioned above the starterelement and is designed to receive a lower end of a shock tube 20, whichcarries the firing signal. A bushing 21 surrounds the lower end of theshock tube 20 where it enters the detonator 10, and the upper end of thedetonator shell 11 is crimped to hold the bushing and shock tube inplace.

FIG. 2 shows an example of an electric detonator 10′. The detonator alsohas a metallic tubular detonator shell 11′ closed at its bottom end andcontaining a base charge 12′ of explosive (e.g. PETN) pressed or casttherein. Immediately above the base charge 12′ is a delay element 14′made of a rigid metal such as zinc, aluminum, steel or brass (preferablyzinc). The delay element 14′ contains an initiating charge 15′ (e.g. oflead azide) at the lower end of the element, and a delay composition 16′within the delay element above the initiating charge 15′. As in theprevious embodiment, the confinement element 14′ and its contents,particularly the delay composition, together form a delay element 14 a′that is formed prior to the assembly of the detonator. A starter element17′, which may also act as a sealer, is located above the delay element,and a lower end of a bore in the starter element contains a startercharge 18′. A hollow plastic tube 25 is positioned above the starterelement 17′ and contains an electrically operated fuse head 26 attachedto leg wires 27 that exit the detonator and that convey the electricalfiring signal. A bushing 21′ is positioned above the plastic tube 25 andhas holes through with the leg wires may pass. The upper end of thedetonator shell 11′ is crimped around the bushing 21′ to hold the legwires and detonator contents securely in place.

As already noted, the delay compositions of the invention areparticularly suitable for creating long delay periods, e.g. more thanone second; preferably 1 to 12 seconds, more preferably 1 to 9 seconds,and most preferably 2 to 9 seconds. In order to produce delay elements,detonators, delay devices, and the like, of acceptable length (normallyno longer than about 1.5 inches), this means that the compositionsshould preferably have a burn rate (burn duration) in the range of atleast 1500 milliseconds per linear inch, more preferably 2,000 to 7000milliseconds per linear inch, and most preferably about 4,000 to 6,000milliseconds per linear inch, and ideally 5,000 to 6,000 millisecondsper linear inch. In contrast, in the experience of the inventor of thepresent invention, the burn rates of those compositions of U.S. Pat. No.4,419,154 that contain red lead fall in the range of about 300 to 1500milliseconds per linear inch when they contain similar amounts ofsilicon of similar particle size to those of the present invention.

As noted above, the delay compositions of the present invention containabout 3 to 15% by weight of particulate red lead in addition toparticles of silicon and barium sulfate. More preferably, the amount ofred lead is 6 to 12% by weight, and most preferably it is 9 to 12% byweight. If the percentage of red lead is increased much beyond about 15%by weight, the burn rate becomes excessively fast for long delays,whereas if the percentage is less than 3%, there are no benefits interms of robustness of combustion and reliability. Although the amountof red lead is much less than previously employed in compositions ofthis kind (e.g. as disclosed in U.S. Pat. No. 4,419,154), it has beensurprisingly found that the amount is sufficient to impart suitablerobustness and reliability of combustion to the composition when used inrigid metal confinement elements, without increasing the burn rateunacceptably for long delay uses.

The red lead used in the compositions of the present invention does notact as a flux. Without wishing to be bound by any particular theory ofoperation, the red lead appears to react with silicon at a low ignitiontemperature (about 500° C.) and generates heat which facilitates thebarium sulfate/silicon combustion reaction whose ignition temperature ishigh (about 1200° C.).

In the compositions of the invention, the relative proportions of thesilicon and barium sulfate are preferably 40 to 65% by weight bariumsulfate and 25 to 50% by weight silicon (this corresponds to 45 to 70%by weight of barium sulfate to 30 to 55% by weight of silicon before theaddition of the red lead). Preferably, except possibly for a binder(described below), no other materials are present in the composition.While the presence of fluxes can be tolerated, there is no particularadvantage to their use in the present invention and their use merelyadds cost.

The compositions of the present invention may be prepared simply by drymixing particles of the essential ingredients in the indicatedproportions. In the case of the barium sulfate, the particulate startingmaterial preferably has a specific surface area of typically about 0.8m²/g (e.g. about 0.75 to 0.85 m²/g). The silicon powder preferably has aspecific surface area of about 6 to 8 m²/g. The red lead preferably hasa particle size of about 1 to 3 microns.

Although dry mixing of the ingredients is possible, wet mixing ispreferred in order to achieve greater homogeneity and because wet mixingallows for the addition of a binder whose function is to agglomeratecollections of individual particles into larger free-flowing granules.Suitable binders include solvent-soluble polymers, fine silica andfinely ground swelling clays. While polyvinylchloride may be used as abinder, it is more preferable to use a water-soluble form of cellulose,e.g. nitrocellulose or, most preferably, sodium carboxymethyl cellulose(e.g. as manufactured by a European subsidiary of Hoechst and sold underthe trademarks TYLOSE and TYLOSE C-600). This material is a sugar-likepowder that is dissolved in water and then used for the wet mixing step.Standard methods of wet mixing, granulation and drying may be employed.As noted, the presence of a binder makes it possible to produce thecomposition in the form of free-flowing granules made up of collectionsof particles of silicon, barium sulfate, red lead and binder.Free-flowing granules have the ability to flow freely (i.e. withoutclumping in the nature of dry sand) when poured from one container toanother. This ability is highly preferred given that the compositionmust be introduced into the interior of a rigid confinement element ofnarrow interior diameter (e.g. typically about 3.35 mm) and thencompacted. It is also an advantage that the agglomerated granules eachtend to contain particles (of all of the main constituents) with a rangeof particle sizes. The homogeneity of the resulting composition istherefore very high and there tends to be little separation of large andsmall particles when the composition is subjected to storage or use overa long period of time. The binder, when present, is preferably containedin the resulting composition (when dry) in an amount in the range of 0.2to 0.6% by weight, more preferably 0.3 to 0.5% by weight, of the totalcomposition. With amounts more than 0.6% by weight, the granulationprocess becomes difficult. When the amount is less than about 0.2% byweight, the binding effect may become inadequate.

After formation and drying, the composition is introduced into a rigidmetal confinement element, as noted, and is compacted therein, usuallyby introducing a metal rod into one end of the confinement element andpressing while preventing the composition from escaping from theopposite end of the tubular confinement element. Pressing from both endsmay, of course, also take place. The resulting composition in theconfinement element preferably has a density falling within the range of1.90 to 2.20 g/cc, most preferably 1.95 to 2.15 g/cc. Compaction to asuitable density is important to ensure reliable propagation ofcombustion, although the desired density may vary somewhat fromcomposition to composition.

The presence of red lead in the delay composition in the indicatedamounts does not alter the essential character of the Si/BaSO₄ mixtureas a slow delay composition (i.e. it does not substantially speed up orslow down the burning rate) but its presence does impart to thecomposition resistance to quenching caused by the heat-sink effect ofthe tubular metal confinement element, so that the composition iseffective in rigid elements such as zinc elements.

Rigid elements containing the compositions of the invention have shownthemselves in tests to be effective as reliable, reproducible delayelements within the confines of standard detonator shell dimensions usedin the art while providing delays of more than one second, e.g. fromabout 2 seconds to optimally 9 seconds or even higher. The rigidelements tested were in fact zinc elements, being the presentlypreferred metal for rigid confinement elements, but may of course havebeen made of another suitable material, e.g. aluminum, steel or brass.

In the most preferred forms, the delay compositions of the inventionconsists only of silicon, barium sulfate, red lead and optionally abinder in the indicated amounts, i.e. there are no other materials suchas oxidants and fluxes, except for incidental or adventitious minorimpurities or ingredients.

The invention will now be further described by way of the followingExamples which are illustrative of delay compositions according to theinvention, and of detonators and delay devices, also according to theinvention. The Examples should, not be taken as limiting the broad scopeof the invention as defined by the accompanying claims.

Example 1

Small quantities (10 g samples) of dry mixed BaSO₄/Silicon compositionswere prepared containing 3%, 5%, 7%, and 9% by weight of Pb₃O₄.

Rigid zinc tubular confinement elements having bore diameters of 3.35 mmwere loaded with each of the compositions, as well as a controlcontaining no Pb₃O₄. The loaded rigid confinement elements wereassembled into detonators for testing. It was found necessary to use aPb₃O₄/Si starter composition on top of the BaSO₄/Silicon/Pb₃O₄ mixturefor reliable ignition. A pyrotechnic sealer element was placed on top ofthe starter element. These detonators were assembled as shocktube(non-electric) detonators and tested for average delay timing andcoefficient of variation (CV). The results of the tests are shown inTable 1 below. The 5% and the 7% Pb₃O₄ samples showed a noticeableimprovement in timing accuracy compared to the control containing noPb₃O₄.

TABLE 1 Pb₃O₄ AVERAGE DELAY COEFFICIENT OF CONTENT TIMING VARIATION 02687 ms 2.1% 3 2800 ms 1.6% 5 2756 ms 0.9% 7 2737 ms 0.8% 9 2716 ms 1.4%

The robustness of propagation of the composition was measured by testingcomposition ignition at −40° C. Rigid confinement elements of the abovekind were prepared containing BaSO₄/Silicon and 6% Pb₃O₄. As before,these elements were assembled into non-electric detonators. Testing ofthe detonators after exposure to a temperature of −40° C. for 48 hoursshowed reliable functioning with timing accuracy as good as a controlsample tested at room temperature, while ⅘ detonators made withBaSO₄/Silicon failed to propagate through the delay column. During thecourse of ambient temperature testing of rigid elements containingBaSO₄/Silicon and no Pb₃O₄, a number of failures (⅖) were recorded wherethe BaSO₄/Silicon column failed to propagate. These failures serve toshow that the addition of a small amount of Pb₃O₄ does indeed impart asignificant improvement to this composition without substantiallyincreasing the combustion propagation rate.

It has thus been demonstrated that the addition of a small amount ofPb₃O₄ to a BaSO₄/Silicon pyrotechnic mixture results in a new improvedcomposition which show improved performance in rigid elements.

Example 2 Dry Mix

production mix sample of standard barium sulfate/silicon compositioncontaining 45% by weight of silicon and 55% by weight of barium sulfate(referred to as Y composition) was first divided in 5 small mixes of 10g each in a small Velostat™ (electrically conductive polymer) container.The first sample was left intact as a reference control sample while anaddition of 3%, 5%, 7%, and 9% of red lead was made in the subsequentmixes. Conductive rubber balls were added to the mixes to help theingredients to mix together during tumbling of the Velostat™ containers.

Wet Mix:

A 1 Kg batch of a modified standard barium sulfate/silicon composition(Y composition) having 6% red lead in it was prepared. The respectivemass ratios for the ingredients were 51.7% of BaSO₄ (0.8 m²/g surfacearea), 42.3% Silicon (milled for 12 hours) and 6% of Pb₃O₄. Although thered lead was added to the medium from the start to ensure a gooddispersion of particles, a regular wet mixing process for standardbarium sulfate/silicon composition was followed.

Tests:

The compositions (both of the dry mix and the wet mix) were tested forignition by friction. None of the compositions containing red leadshowed signs of ignition when tested for friction sensitivity using a1.33 kg steel torpedo sliding with 30° angle from 30 inch height.

The differential thermal analysis (DTA) of a composition containing nored lead and a composition containing 5% red lead showed that thepresence of red lead in the standard barium sulfate/silicon compositionreduced the ignition point of the composition, which facilitatedignition of the powder.

Methodology Of Powder Loading In Zinc Element

A zinc confinement element was weighed, placed in a holder and a delaycomposition of the invention was poured into its cavity and pressed atthe desired pressure in many small increments until full. The elementwas weighed again and the powder content recorded. The reliability(standard deviation SD) of powder content in elements was found good forboth element lengths evaluated, as shown in Table 2 below.

TABLE 2 Element Length Charge Weight Sample Size SD 12 mm 201 mg 30 2.130 mm 504 mg 30 6.0Delay Timing “vs” Red Lead Content in Barium Sulfate/SiliconCompositions.

The graph of FIG. 3 shows that the presence of red lead in a standardcomposition of barium sulfate/silicon (55%:45% by weight) has first, aneffect of slowing down the burn rate with the 3% addition of red leadand slight speed increases with the higher red lead content.

The delay timings were determined in ORICA® 2.9 inch detonator shellhaving a 9.3 mm (0.362″) zinc confinement element as main and a regularstarter and sealer from drawn lead tube.

Deviation in Delay Times “vs” Red Lead Content in Barium Sulfate/SiliconCompositions.

From previous timing results, the graph of FIG. 4 illustrates thecoefficient of variation of measured timing delays.

It can be seen that any barium sulfate/silicon mix that had the presenceof red lead in it produced a better timing accuracy than the controlsample containing no red lead.

The sample size for the above results was only 5 detonators per mix, so,in order to confirm the validity of the delay timing obtained, the mixwith 5% Red Lead was further loaded in 30 zinc confinement elements andin two different element lengths. They were tested for timing accuracyin ORICA® detonator shells and results compared with those obtained byothers for this specific lot of the standard barium sulfate/Sicomposition. The results are shown in Table 3 below (in which SD standsfor standard deviation).

TABLE 3 Zinc element length Average timing SD CV sample size 12 mm 3487ms 54 1.5 30 30 mm 8383 ms 91 1.1 30

In lead elements, the following provided the following timing resultsfor this lot of the standard composition:

1896 ms average with a SD of 71; CV = 3.7% cutting length at 0.305 inch(7.7 mm) 9921 ms average with a SD of 150; CV = 1.5% cutting length at1.318 inch (33.4 mm)

Powder Loading Pressure Effect on Detonator Delay Timing

In order to define the proper range for powder loading in rigid zincconfinement elements, the 5% red lead content mix was loaded in the 9.30mm zinc confinement elements, pressed at different pressure and fired.Although all detonators made with elements loaded at 28 Kpsi failed toignite, the results illustrated in the graphs of FIGS. 5 and 6 indicatedthat powder loading pressure in the range between 3.5 Kpsi to 21 Kpsihave a very little effect on the overall timing results. A better timingaccuracy is observed for those elements loaded at 3.5 Kpsi and 7 Kpsi.

Powder Density “vs” Loading Pressure

The density of the delay composition loaded in zinc confinement elementsand at different pressure was measured for both 5% and 7% red lead mixesthat showed the best timing performances. The results are shown in thegraph of FIG. 7. According to the previous results, it is recommendedthat the powder loading density shall be kept between 1.80 g/cc and 2.20g/cc and more preferably at 1.95 to 2.15 g/cc.

Robustness of Propagation

An evaluation was made to measure the timing shift between +20° C. and−40° C. on various detonator designs in order to demonstrate theadvantage of adding some red lead in barium sulfate/Si composition witheither the drawn lead or rigid zinc confinement element technology. Theresults are shown in the graph of FIG. 8.

Note: All main elements (lead or zinc) were prepared to be in the sameorder of delay timing, between 2800 ms and 3000 ms.

In the graph of FIG. 8:—

-   -   Column 1=Timing shift on barium sulfate/Si composition control        sample in regular drawn lead ORICA® detonator.    -   Column 2=Timing shift on barium sulfate/Si composition+4% Red        Lead in regular drawn lead & ORICA® detonator.    -   Column 3=Timing shift on barium sulfate/Si composition+6% Red        Lead in regular drawn lead & ORICA® detonator.    -   Column 4=Timing shift on barium sulfate/Si composition+4% Red        Lead in zinc main element. Regular starter (red lead+silicon        75:25) and sealer with a small bore element with a composition        of red lead and silicon (63:37) from drawn lead in ORICA®        detonator shell.    -   Column 5=Timing shift on barium sulfate/Si composition+6% Red        Lead in zinc main element. Regular starter and sealer as above        from drawn lead in ORICA® detonator shell.    -   Column 6=Timing shift on barium sulfate/Si composition+6% Red        Lead in zinc main element. 150 mg of red lead+silicon (75:25)        and 100 mg of G comp. loaded in the aluminum type 2 sealer in        DNES® detonator shell.    -   Column 7=Timing shift on barium sulfate/Si composition+6% Red        Lead in zinc main element. 150 mg of red lead+silicon (75:25)        loaded at first in the main element and 215 mg of G comp. in        aluminum type 2 sealer in DNES® detonator shell.

Although the ORICA® detonator design showed a better timing stability,no failure to ignite was observed on more than 100 detonators fired at−40° C. and having a main element made of zinc.

Example 3

In this Example, the maximum quantity of red lead that can be added tothe barium sulfate/Si composition for a long delay period detonator isidentified and the resistance to shock stop (failure of a detonator dueto the shock from an adjacent explosion) of such systems ischaracterized for both, drawn lead and rigid confinement elementtechnology.

All mixes used for the delay timing evaluation are from small dry mixeswhere red lead was added in various quantities in barium sulfate/Si. Theingredients were put together and tumbled in small Velostat pots withconductive rubber balls.

The mixes used for the shock resistance evaluation were made wet mix inbatch of 700 g.

Powder Sensitivity

Friction Sensitivity

Test Description:

A steel torpedo of 1.33 Kg weight slides on a sample of powder from 30inch height and 30° angle.

No ignition observed in ten trials when the 12% red lead content mix wastested for friction sensitivity.

Other powder samples containing less than 9% of red lead were alsotested for friction sensitivity and did not show any signs of ignitioneither.

Detonator Construction:

In order to avoid sympathetic detonations during shock stop testing, thelead azide charge (110 mg) was pressed inside the zinc element cavity.The rest of the cavity was filled with the delay powder. A regularstarter (red lead+silicon 75:25 by weight) and sealer (sealer with asmall bore element filled with red lead+silicon 63:37 by weight) waspressed on top of the rigid element and a sealer crimp applied.

A low entropy plastic disc (LE disc) was put on top of the lead azidecharge for those detonators made with the main delay elements from adrawn lead rod.

Test Results:

Delay Timing

The graphs of FIGS. 9 and 10 show the delay timing pattern for modifiedbasic barium sulfate/silicon composition with 0% to 20% red leadcontent. A plateau of relatively stable delay times is observed forthose mixes having between 0% and 12% of red lead added in the basicbarium sulfate/silicon composition. FIG. 9 is a graph showing the delaytiming in zinc elements (9.30 mm L) on Y comp+Red Lead content (Estarter & H sealer from drawn lead). FIG. 10 is a graph showing the CV'sfrom delay timing in zinc elements (9.30 mm) on Y comp.+Red Lead content(E starter & H sealer from drawn lead)

Shock Stop—Test Results

A drum test was performed on composition Y and modified comp. Ycontaining 6% and 12% of Red Lead. The LP detonators from DNES (7000 ms)were also tested for shock resistance.

-   Test method used: Cooking mode; meaning that both detonators were    fired simultaneously.-   Delay timings: target: 5000 ms and 7000 ms    -   donor: 2500 ms and 3500 ms

The shock pressure test was performed at 14000 psi (Position #11 intemplate).

Test 1 Main Delay Composition in Rigid Zinc Elements

Control sample of Y comp.: 3/10 failures caused by shock stop. Y + 6% ofRed Lead: 6/10 failures caused by shock stop. Y + 12% of Red Lead: 0/10failure. DNES 7000 ms: 0/10 failure.

Test 2 Main Delay Composition in Drawn Lead Elements

Control sample of Y comp.: 5/10 failures caused by shock stop; 1 failedat the LE disc. Y + 6% of Red Lead: 8/10 failures caused by shock stop.Y + 12% of Red Lead: 6/10 failures caused by shock stop.

Example 4

This Example relates to the use of a binder (carboxymethyl cellulose) inthe preparation of the delay compositions of the invention.

Batches (500 g each) of delay compositions were made from barium sulfate(Type N, having a specific surface area of 0.8 m²/g), silicon (2.6microns in size, from SKW powder company, ground for 12 hours), red leadand sodium carboxymethyl cellulose (TYLOSE® C-600) using a Waringblender. The batches were formed by dissolving a powder of thecarboxymethyl cellulose in 200 ml water in a mixing vessel over twominutes for complete dissolution, adding the red lead and mixing forabout one minute, adding half of the quantity of barium sulfate andsilicon and mixing for two minutes, then adding the remainder of thesilicon and barium sulfate and mixing for a further 2 minutes. The ratioof water to dry ingredients was 40%. The batches contained 6%, 9% or 12%red lead and amounts of TYLOSE from 0.3 to 0.6% by weight. The ratio ofbarium sulfate to silicon (discounting other ingredients) was about55:45 by weight). The mixtures were then dried for a few hours andmanually granulated behind a shield through a 20 Tyler mesh sieve. Theresulting granules were found to flow very well (i.e. freely), e.g. whenpoured from one container to another.

The granulated mixtures were loaded into rigid zinc confinement elementsby placing the zinc elements in a holder and scooping the compositionand pouring it into the element cavity and pressing at the requiredpressure for proper density. This was done in increments until theelement was full. In all cases, the incremental loading was 5.0 mm(pressed). This corresponded to a volume of 90 mg powder for eachincrement. A subsequent test with incremental loading of 3.0 mm (50 mgof powder) produced an even better coefficient of variation (CV) fordelay timing indicating that the procedure benefits by having many smallloading increments for better reliability. It is to be noted that theloading pressure has to be reduced in order to keep the same powderloading density with smaller increments. The results are shown in Table4 below.

TABLE 4 Test # 1 Test # 2 Composition BaSO₄/Si/Pb₃O₄/TyloseBaSO₄/Si/Pb₃O₄/Tylose Incremental loading 5.0 mm pressed 3.0 mm pressedLoading force 150 pounds on punch 100 pounds on punch (12000 psi) (8000psi) Pressed density 2.10 g/cc 2.10 g/cc Average delay of 7369 ms 7399ms timing Coefficient of 2.2% 1.8% variation

Detonator Construction

Detonators were constructed with the rigid zinc confinement elements.These detonators contained a starter comprising a mixture of red leadand fine silicon (so-called E starter) and a sealer (so-called H sealer)prepared with a small bore element made from drawn lead rod containing amixture of red lead and very fine silicon. All the results were obtainedusing ORICA® detonator shells.

Formulation Study

Wet mixes with 6%, 9% and 12% red lead and 0.5% TYLOSE® in Composition Ywere made and assessed in 30 mm zinc elements for detonator timing.

The 6% red lead mix showed 20% detonator failures at room temperature.The 9% red lead mix did not show detonator failure at room temperature,but 50% detonators failed when fired at low temperature (−40° C.). The12% red lead mix showed no failures at −40° C. and was selected for thefollowing extended characterization.

Delay Time vs. Length of Element

The burn rate of the composition in zinc elements was found to be verylinear, even at low temperatures (−40° C.). The graph of FIG. 11 showsthe delay time pattern for the long period (LP) compositionBaSO₄/Si/Pb₃O₄/TYLOSE (48/39.5/12/0.5% by weight) versus the elementlength.

Delay Time vs. Loading Pressure

The graph of FIG. 12 shows the delay time pattern forBaSO₄/Si/Pb₃O₄/TYLOSE (48/39.5/12/0.5% by weight) in 44 mm lengthelements.

Delay Time vs. TYLOSE Content

The graph of FIG. 13 shows that the addition of Tylose slows down thecomposition burn rate. The loading pressure was kept constant at 12000psi in 44 mm zinc elements.

Testing at Low Temperature

A stress test was widely used in this evaluation in which the detonatorwas frozen in ice for 16 to 24 hours and fired within one minute. Inorder to give confidence to this test FIG. 14 shows the “warming up”curve for a sample taken out of the freezer for five minutes.

Robustness of Propagation

The powder loading density is an important factor for the composition.This was found to be particularly true when detonators were fired at lowtemperature.

The graph of FIG. 15 shows the failure rate versus powder loadingpressure (psi) for BaSO₄/Si/Pb₃O₄/TYLOSE (48/39.5/12/0.5% by weight)loaded in 44 mm zinc elements fired at −40° C.

The graph of FIG. 16 shows the number of detonator failures recordedwhen fired at −40° C. TYLOSE contents of 0.3, 0.4 and 0.5% by weight didnot cause failures.

Timing Shift

The graph of FIG. 17 shows the timing shift between +20° C. and −40° C.for long period composition BaSO₄/Si/Pb₃O₄/TYLOSE in 44 mm zincconfinement elements and for regular ORICA® and DNES® long perioddetonators.

long period detonators.

The graph of FIG. 18 shows the coefficient of variation on delay timingat −40° C. for the BaSO₄/Si/Pb₃O₄/TYLOSE composition pressed at 12,000psi in 44 mm zinc element, and for regular ORICA® and DNES® long perioddetonators.

Pressed Density

The pressed density of composition BaSO₄/Si/Pb₃O₄ in 44 mm length zincelements versus TYLOSE C-600 content is shown in FIG. 19. The loadingpressure was kept fixed at 12000 psi.

The pressed density of composition BaSO₄/Si/Pb₃O₄/Tylose in zincelements of 44 mm length is shown in FIG. 20. Here the TYLOSE contentwas kept fixed at 0.5% by weight.

Resistance to Shock Stop

A drum test was performed on the following detonator samples:

ORICA® LP 19

DNES® 7000 ms

-   -   Composition containing red lead+0.5% TYLOSE in 30 mm length zinc        elements.

The donor detonator was an ORICA® LP 10 (3500 ms delay) for all tests.

The shock pressure test was performed in “cooking mode” meaning thatboth detonators, the donor and the target, were fired simultaneously.The results are shown in Table 5 below:

TABLE 5 Detonator sample 12000 psi 14000 psi ORICA LP 19 5/10 failuresnot tested DNES 7000 ms 0/15 failure 0/15 failure New LP in zinc 0/15failure 2/15 failures

The above results show that at least a preferred composition made ofbarium sulfate/silicon/red lead (12 hours ground)/TYLOSE® C-600 withrespective mass ratios of 48/39.7/12/0.3% loaded into rigid zincelements at a density of 2.08 g/cc±0.05 g/cc was found to have equal, ifnot superior, detonator performance compared to regular long delaydetonators using lead confinement elements.

1. A delay composition comprising mixed particles of silicon, bariumsulfate and red lead, the red lead being present in an amount of about 3to 15% by weight of the composition.
 2. The composition of claim 1wherein the red lead is present in an amount of about 6 to 12% by weightof the composition.
 3. The composition of claim 1 wherein the red leadis present in an amount of about 9 to 12% by weight of the composition.4. The composition of claim 1 wherein the composition contains about 40to 60% by weight of said barium sulfate and about 25 to 50% by weight ofsaid silicon.
 5. The composition of claim 1 further containing a bindercausing collections of said particles to bind together in the form offree-flowing granules.
 6. The composition of claim 5 wherein said binderis selected from the group consisting of solvent-soluble polymers,silica and swelling clays.
 7. The composition of claim 5 wherein saidbinder is a water-soluble derivative of cellulose.
 8. The composition ofclaim 5 wherein the binder is carboxymethyl cellulose.
 9. Thecomposition of claim 8 wherein said binder is present in an amount of0.2 to 0.6% by weight of the composition.
 10. The composition of claim 1wherein the particles of barium sulfate have a specific surface area ofabout 0.8 m²/g, the particles of silicon have a specific surface area of6 to 8 m²/g, and the red lead has a particle size of about 1 to 3microns.
 11. A delay composition in the form of free flowing granuleseach consisting essentially of mixed particles of silicon, bariumsulfate and red lead, together with a binder, the red lead being presentin an amount of about 3 to 15% by weight of the composition. 12.-29.(canceled)